First off, let’s take a look at how this project, which resulted in this Online Book, started.
About eight years ago, we switched to Absorbed Glass Mat (AGM) batteries on Morgan’s Cloud, to get the following benefits over liquid filled lead-acid batteries:
- Shorter recharge times since AGM batteries accept a faster charge rate.
- No risk of the batteries freezing when we lay-up the boat unattended since AGM batteries have a very low self-discharge rate. (A fully charged battery won’t freeze but a flat one will.)
- About 10% more capacity in the same size battery.
However, our experience with AGM batteries was not good: We went through four sets of house batteries from two different manufacturers after the switch to AGM. When you consider that AGM batteries are as much as double the price of liquid filled batteries, that stung.
In the process of solving that problem, we learnt a huge amount that can be applied to the care of any lead-acid battery.
We should state at this point that we are tough on batteries. At anchor, when we are usually writing and working on photographs, we use as much as 300 amp hours at 12 volts (3.6 kWh) per day for lighting and computers and about the same on passage what with the autopilot, navigation electronics, and lights.
And to make matters worse, due to space constraints, our house bank only totals 510 amp hours—about half the ideal size, given our usage.
In fact, it is likely that our bad experience with AGM batteries had little to do with our change to that technology, since said change coincided with a huge increase in our electricity usage due to the demands of this web site.
We Did The Right Things
However, although our usage is tough, we were doing all the things that are supposed to preserve batteries:
- We never discharged our batteries more than 50%.
- We installed chargers and a regulator that have temperature sensors and purport to be designed to properly charge AGM batteries.
- We always recharged to at least 85%.
But, even so, the last set of AGM batteries died after less than a year and so we had pretty much decided to go back to liquid filled batteries. However, before we did that, we wrote to the manufacturer stating our concerns. What a pleasant surprise to get a helpful and concerned email from Justin Godber of Lifeline Batteries. A big contrast to the usual blow off or, worse yet, dead silence that we are used to getting when we complain about gear that has not met our needs.
So we cut a deal with Justin: He provided us with a new set of AGM batteries for free and committed to advising us on their care and feeding. Our part was to write about the experience and develop a real-world set of recommendations, a manual if you will, on the use and care of lead-acid batteries on a voyaging boat.
This Online Book is the result. We also received a huge amount of wisdom in the form of comments to the original posts, which we have incorporated into this Second Edition.
As we conducted a technical and detailed email exchange with Justin to try and figure out what had killed our batteries so early and how to avoid it happening again, it soon became apparent that we liveaboard voyagers are set up to fail as caretakers of any lead-acid batteries, not just AGMs, for the following reasons:
- The yachting press and most battery experts have told us that you should not equalize AGM batteries. Wrong—any lead-acid battery of any type will sulfate with typical liveaboard use and eventually fail if you don’t get rid of that sulfation regularly with equalization. So, if you can’t equalize a battery, it does not belong on a voyaging boat.
- Many, perhaps most, chargers and alternator voltage regulators are programmed incorrectly as they come from the factory.
- Many chargers simply don’t behave the way they say they do in their own brochures and manuals—yes, even the fancy three stage ones.
Worse still, the general instruction from manufacturers and battery experts, that all you need to do to enjoy a long life from lead-acid batteries is to fully charge them after every discharge, is completely impractical. Here’s why, based on our own installation, but the fundamentals will be the same for any boat: It takes two hours of generator or one hour of main engine time on Morgan’s Cloud to bring our house bank from a 50% discharge state to a 85% charge, but four more hours of charging to get from 85% to 100%.
This same basic fact will apply no matter how powerful your charging source is since the limiting factor is the amount of current (amps) that a battery can accept for the last 20% of its charge cycle.
So this “standard wisdom” is fine if you are in a marina and can plug in, but totally impractical on a voyaging sailboat that may not see shorepower for months at a time and that discharges the batteries by 50% on most days at anchor or at sea, since no one in their right mind is going to run a main engine or generator lightly loaded for five to six hours a day to reach full charge.
What’s Full Charge?
Before we go any further, it is vital that we clearly define what full charge is and how to measure it. Read this carefully because understanding this one fact is vital to managing batteries:
A lead-acid battery is fully charged when the current (amps) it will accept at its specified acceptance voltage—typically about 14.4 volts at 70F (20C)—has dropped to 1-2% of the total capacity measured in amp hours. This is the only practical way to know that a battery is charged.
Amp counters, voltage measurement at rest, and other methods are approximations at best and, if you rely on them, you will almost certainly get less life out of your battery than it’s capable of supplying. The only way to accurately measure charge amps is to have an amp meter with a shunt on the positive side of the battery. More on that later.
Before we go any further, it is important to mention that wind and/or solar power can help to bring your batteries up to full charge every day. But only if you have enough charging capacity to both supply your needs during the day and replace whatever you took out of the battery the night before. That’s a lot of alternative energy, the installation of which will often result in an unseamanlike festooning of the boat with solar panels and wind generator(s). To learn more about alternative energy read Colin’s excellent Online Book Alternative Energy for Voyaging Sailboats.
Real World Tested
But even if you do have that much alternative energy generation capability, applying the techniques you will learn from reading this book will make your batteries last even longer. We know this because we are now getting great service from our batteries, even with our brutal use and undersized house bank.
Justin bought one of my prints for his office wall and he, as stated above, provided two 8D AGM batteries at no cost to us. Those are the only benefits we have received from Lifeline Batteries.